Corrosion of metallic components in plants may cause system failures and sometimes plant shutdowns. In addition, corrosion products accumulated on the metal surface will decrease the rate of heat transfer between the metal surface and the water or other fluid media, and therefore corrosion will reduce the efficiency of the system operation. Therefore, corrosion can increase maintenance and production costs.
The most common way to combat corrosion is to add corrosion inhibiting additives to the fluid of such systems. However, currently available corrosion inhibiting additives are either non-biodegradable, toxic, or both, which limits the applicability of such additives.
The most common anti-corrosion additives used in connection with boiler condensate systems are neutralizing amines and filming amines. While amines and combinations of amines generally provide effective protection against the corrosion of steel and other ferrous-containing metals, the use of amines in anti-corrosion additives presents several problems.
First, amines often undergo thermal decomposition at high temperatures and form ammonia, which can be very corrosive to copper and copper alloys, especially in the presence of oxygen. Thus, amine-containing corrosion inhibitors are often unsatisfactory for use in systems containing copper or copper alloy metallurgies.
Further, in a number of applications including food processing, beverage production, co-generation plants, and pharmaceutical manufacturing, the use of amines is limited due to governmental regulations or concerns for taste and odor problems. Consequently, in many of these applications, no anti-corrosion treatment program is used at all. Therefore, these systems are susceptible to high corrosion rates, significant maintenance costs and high equipment failure rates.
U.S. Pat. No. 5,368,775 discusses methods of controlling acid induced corrosion. In one method, a thin film is used as a barrier between the metal surface to be protected and the acidic solution. Long chain amines such as octadecyl amine or azoles are used to form the thin film. The second method requires the addition of neutralizing amines to neutralize the acid and raise the aqueous pH. The best amines for this method are described as having a high basicity and a low molecular weight. Cyclohexylamine, dimethylamine, trimethylamine, morpholine, and methoxypropylamine were cited as examples of neutralizing amines.
U.S. Pat. No. 4,915,934 discloses a foamable biocide composition comprising an alcoholic chlorohexidine solution, quick breaking foaming agent, an aerosol propellant, and corrosion inhibitor to counter the corrosive nature of the alcoholic chlorohexidine solution. The quick breaking foaming agent contains, as one of its ingredients, a surface active agent, preferably an ethoxylated sorbitan ester. The surface active agent acts as an emulsifier. Examples of the preferred emulsifier given include ethoxylated sorbitan stearate, palmitate, and oleate; nonyl phenol ethoxylates; and, fatty alcohol ethoxylates.
U.S. Pat. No. 3,977,994 discloses a rust inhibiting composition. The composition is a mixture of an organic acid, an N-alkyl or cycloalkyl substituted ethanolamine, and water. In some cases, the composition may also contain at least one emulsifying agent to permit the emulsion of the organic acid and the ethanolamine. Examples of the emulsifying agent include sorbitan derivatives.
U.S. Pat. No. 4,970,026 teaches a corrosion inhibitor for ferrous and non-ferrous aqueous systems. The composition comprises a component selected from a naphthenic oil based sodium salt of a triethanolamine alkylsulfamido, carboxylic acid; a paraffinic oil based sodium salt of a triethanolamine alkylsulfamido carboxylic acid; a sodium salt of an alkylsulfamido carboxylic acid; and a mixture consisting of two choices as well as a surfactant selected from a long chain fatty acid derivative of sarcosine and a condensation product of ethylene oxide and a fatty acid.
The inhibiting effects are attributed to the component or mixture of components, not to the addition of the surfactant. In fact, the patent states that the surfactants were tested separately for their effectiveness as corrosion inhibitors. The surfactants were found to be ineffective as corrosion inhibitors.
U.S. Pat. No. 5,082,592 discloses a method for inhibiting corrosion for ferrous metals in aqueous solution comprising a nonionic surfactant and an anionic oxygen containing group such as alkali metal salts of borate, molybdate, and nitrate/nitrite. The preferred nonionic surfactant is phenol/polyethylene oxide.
It is postulated in the specification that the nonionic surfactant increases the corrosion inhibition properties of the anions. The inhibition properties of the anions result from their adsorption at the interface of the metal surface and the solution. It is believed that the co-absorption of the nonionic surfactant serves to maximize the surface concentration of the anions by shielding the anions' hydrostatic repulsive forces.
EPO Patent Application, No. 0 108 536 B1 discloses a method for protecting metal surfaces from corrosion. The method uses a composition of a corrosion inhibitor with a thickening agent. The corrosion inhibitor may include carboxylic acid esters of sorbitan. In combination with a thickening agent, the corrosion inhibitor is pseudoplastic and thixotropic. The composition forms a gel upon standing. The composition forms a soft, flexible coating which can replace paints, varnishes, lacquers, plastics and metal coatings frequently used to protect metal surfaces from corrosion.
Therefore, there is a strong need for a corrosion-inhibiting non-amine, less toxic additive which is a more environmentally acceptable alternative. In the present invention, a phosphoglyceride compound surprisingly provides protection of metallic surfaces from corrosion in aqueous and non-aqueous solutions.